According to 3GPP Technical Specification 25.331, when a user initiates a call on user equipment (UE) such as a radiotelephone, laptop with wireless connection, or wireless messaging device, an RRC Connection Request message is sent by the UE to the network to trigger the establishment of a radio resource control connection. The network then assigns radio resources to the UE and sends an RRC Connection Setup message to direct the UE to properly configure its signaling radio bearers. After the UE has configured its radio resource control connection, the UE sends an RRC Connection Setup Complete message to the network.
After the network receives the message that the radio resource control connection is properly configured, the network sends a Radio Bearer Setup message to direct the UE to properly configure its user radio bearers. Once the user radio bearers are properly configured, the UE sends a Radio Bearer Setup Complete message to the network. Because this message is sent in Acknowledgement Radio Link Control (RLC) mode, the network sends an RLC protocol layer ACK to the UE upon reception of the Radio Bearer Setup Complete message.
If a radio link failure, such as a signal fade or excessive signal noise, occurs during or after the RRC layer in the UE submits a Radio Bearer Setup Complete message to its lower layers for transmission to the network, the network will not receive the Radio Bearer Setup Complete message and the network will not send an RLC layer ACK. Upon radio link failure, the UE will send a Cell Update message with a cause of “radio link failure.” Because the network did not receive a Radio Bearer Setup Complete message from the UE, the network will assume that the UE failed to properly configure its radio bearers in accordance with the earlier Radio Bearer Setup message from the network. This could lead to the network and the UE getting out of sync with respect to the configurations used at their respective ends—eventually leading to a call drop.
If a radio link failure, such as a signal fade or excessive signal noise, occurs after the network has received the Radio Bearer Setup Complete message, the UE will also send a Cell Update message with a cause of “radio link failure.” In this situation, the network will assume that the UE configured its user radio bearers in accordance with the earlier Radio Bearer Setup message from the network, the network and the UE will be in sync, and the call will continue.
Thus, depending on the exact timing of a radio link failure following a UE configuring its radio bearers, a call could drop or continue. There is an opportunity for the UE and the network to maintain a call more consistently after a radio link failure during or shortly after configuration of a UE's radio bearers. The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Drawings and accompanying Detailed Description.